Perl - Leonid Mamchenkov

RegExp reminder

I was just reminded about this small thing, which is so easy to forget – regular expressions that have markers of line start (^) and/or line end($) are so much faster than those regexps that don’t have these markers. The thing is that with line start/end marker regexp engine needs to make only one match/substution, whereas when there is no such markers, it has to repeat the match/substitution operation at every character of the string.

In practice, it’s unbelievable how much difference this can make. Especially when using complex regular expressions over large data sets.

P.S.: I understand that it is not always possible to use these markers, but I think that they can be used much more often than they are. Everywhere.

The answer to “Why Not Python?”

Collin Park has written an article in four parts (one, two, three, and four) titled “Why Not Python?”. I’ve read through the first couple of parts and scrolled through the rest.

In all that text that passed in front of my eyes I haven’t found the answer to the question. I guess, it wasn’t actually the question after all then.

Well, in case you read asked yourself “Why Not Python?”, I’ll give one of the possible answers. Because it is too complicated. Python might do OK as the first progarmming language for those of you who want to learn programming concepts. But if you have a problem at hand that needs solving, Perl is the way to go in most of the cases.

Example. Collin Park uses the Sudoku game solver as one of the examples. Fine task. Nice one to learn how to program too. But if you just have a Sudoku game to solve (or a few for that matter), than it would be much faster to do it in Perl. Here is how.

Navigate your browser to search.cpan.org.
Type in “sudoku”, choose “Modules” and press “Search CPAN”.
With this particular example, any module from the search result can be used. With other examples, you want really want to review the module description (one line that says what module does). So, this step is, choose the one module that seems to be appropriate for your problem.
Install chosen module, by running cpan command from root shell and typing in install module::name (substitute “module::name” with the name of the module you chose in the previous step).
Run perldoc module::name to see module documentation and example of used.
Copy the code from SYNOPSIS are of documentation in your favourite editor.
Save the file
Run the script

Tada! You’re all done.

If it takes you more than 15 minutes, chances are – you are doing something wrong. Of course, your mileage may vary, but 15 minutes is somewhere near the lighthouse.

Decimal to binary convertion in Perl

This is a simple thing, but when you need it – you need it. There is no need in implementing a function that does or looking for a module at CPAN. All you are looking for is already there.

#!/usr/bin/perl -w

use strict;

# Get the number from the command line or use default.
my $number = shift || 42;

printf "%b\n", $number;

You might want to refresh you memory of printf or sprintf by flipping though the manual pages.

P.S.: 42 decimal = 101010 binary. Is it cool or what?

Perl modules of the day

I’ve been doing a whole lot of Perl recently. Because of that, I spent a lot of time at CPAN. As a result, I came across a few excellent modules that I didn’t know about before. Here is a round-up for you:

Devel::ebug – Perl debugger, than can be used from the web and from the scripts.
Class::DBI::Sweet – some really useful stuff for Class::DBI users.
DBIx::Class::CDBICompat – compatibility layer between Class::DBI and DBIx::Class. In case I’ll ever move to DBIx::Class.

Also I have to express my amazement with XML::RSS, which goes far beyond RSS documents and parses almost any XML document. Outstanding job!

Missing some regexp knowledge

Once in a while I come across some topic that I should have learned a billion years ago. Something very basic and useful that I had a chance of seeing many times but haven’t, or probably had and ignored it. Today I found out that I was missing an important bit of Perl regexp knowledge. And you will probably laugh in my face when I’ll tell you.

Continue reading Missing some regexp knowledge